Amplifier circuits



Patented Jan. 10, 1928.

UNITED STATESn PATENT OFFICE.

JOHN W. FOLEY, QF IIBOGOTA, NEW JERSEY, ASSIGNOR T WESTERN ELECTRICvCOMI- PANY, INCORPORATED, OIF NEW YORK, N. Y., A CORPORATION 0F NEWYORK.

AMPLIFIER CIRCUITS.

.application led January 18, 1926. Serial No. 82,079.

This invention relates to telephone subsets, and has for an object toprovide means energized from a central source for amplitying thereceived, or both the received and transmitted signals. Y

It is often desirable to equip a subscribers set for amplifying receivedor both the received and transmitted signals. `Electron dischargeamplifiers are very suitable for this apparatus and it is desirable thatthe .devices be energized from a central source.

In accordance with a feature of this invention, a thermionic amplilieris provided for amplying the received energy at a subscribers set. Meansare provided for supplying both the iilament heating current and thespace current to this device from a central source. In addition, currentis supplied to the transmitter from the same source;

In accordance with another feature of this invention, a thermionicampliiier energized Jfrom a central source is provided for amplifyingboth the received and transmitted energies.

The invention will be morereadily understood by reference to thefollowing description in connectionv with the drawing in which: Figs. 1,2, 3 and 4 show telephone systems embodying subscribers sets arand Fig.5 shows a system embodying a set arranged kfor amplifying both thereceived and transmitted slgnals. A

In Fig. 1 the subscribers sets A and B are connected by lines 6 and 7 toa central sta tion C which comprises the usual central stationsequipment including a common battery 8 ,and repeating coil 9. At thesubscribers station A the telephone transmitter 11 of the push-pull typeis operative through a repeating co'il 12 to impress speech variationsonto the line 6. An ainpliiier 13` is provided which is connected to theline 6 through the input transformer 14 and having a receiver 1 5connected to its output terminals. central source 8, condensers 16 and17 and retard coil 18 being provided for controlling the paths of thecircuit and f signaling current in a manner described below. Aswitchhook 25 and a call bell 26 are'also provided. The switchhook 25operates to deenergize the tube 13` by breaking the filament circuitranged for amplifying the received signals;

The tube 13 is'energized from the when held in the down position by theweight of the receiver. The calling bell 26 is connected in seriesrelation with the c0n,

denser 16 across line 6, the bell and condenser being so proportioned asto respond to curents of ringing frequencies sent over the lne.

Transformer 14 -.is of the usual step-up type for efficiently operatingthe tube 13.

-When the switchhook 25 is closed, direct current iiows from thepositive terminal of `the battery 8 over line- 6 through the two sidesof transmitter 11 in parallel, transformer 12, rheostat 27, retard coil18, filament 28 of the vacuum tube 13, grid biasing resistance 29 andthe primary of transformer 14 back over line 6 to the negative terminalof the battery 8. This current energizes the lilament 28 and makes thetransmitter 11 operative. The-rheostat 27 isprovided jor the purpose ofcontrolling the lilament current of the tubes. The grid of the tube 13is maintained at a negative potential with respect to the filament bythe drop inthe re- Y sistance 29.

The space current of the tube can be traced from the positive terminalof thebattery 8 through the calling bell 26, thereceiver 15 to theplate30 of the tube 13,- filament 28, resistance 29, primary7 winding ofthe trnsformer 14 and back over line 6 to the negative terminal of thebattery. The inductive eiiect of the bell winding. 26prevents the flowof signalingcurrent through this circuit. Condensers 16 and 17 providepathsfor the signaling current in the output circuit of the tube and thetransmitter circuit respectively, while at the same time conning thedirect current in the plate and filament to the proper paths. i

Subscriber set B is not shown in detail but may be similarly arranged orof any suitable type. Y

Fig. 2 shows a similar system except that in this subset circuit asingle acting transmitter 32 is provided in place of the ushpulltransmit-ter 11. The central station C is merely indicated, the batteryand repeat ing coils not being shown in detail. lThe direct current flowin this circuit may be traced from the positive terminal of the centralbattery over the line 6 through switchhook 25,

transmitter button 32, filament 28, resistance 29, primary winding ofthe transformer 14, rheostat 27 over line 6 baclr to the negativeterminal o-f the central battery. The space current circuit is the sameas that for the system shown in Fig. 1.

` Fig'. 3 shows an anti-side tone subscribers set of the type shown inFi of U. S. Patent 1,255,472 granted to A. Campbell, January 22, 1918.The element 33 is provided for balancing the line. It usually consistsof a resistance and is incorporated in the transformer Winding. When thetransmitter 32 is operated, it energizes both Windings 35 and 36 of thetransformer 34, part of the energy being transmitted over the line 6 andthe other part dissipated in the element 33. The current in these twowindings being opposed, no energy is transmitted through the tube 13 tothe receiver 15.

The filament heating circuit vfor this set :may be traced from thepositive terminal of t-lie central battery over line 6 to switchhookwhere it divides, the main portion flowing through the transmitter 32while the rest flows through resistance 33 and winding 36 to the retardcoil 18, filament 28, resistance 29, connection 37, rheostat 27 backover the line v6 to the negative terminal of the central battery. Theplate current can be traced from the positive terminal of the centralbattery over the line 6, through Winding of the calling bell 26,receiver 15, anode 30, filament 28, resistance 29, connection 37,rheostat 27, back over the line 6 to the negative terminal of theccntralbattery.

The set in Fig. 4 is similar to that of Fig.

i 3 except that -the retard coil 18 is omitted,

` `and part of the talking current is permitted to flow through thefilament. In this case, the filament heating circuit may be `traced fromthe positive terminal of the central battery over line 6, throughswitchhook 25,

transmitter 32 in parallel with resistance 33 and winding 36 in series,winding 35 of the primary winding of transformer 34, connection 38,filament 28, resistance 29, connection 37, rheostat 27 baclrover theline 6 to the negative terminal of 'thie central battery. The greaterportion of the talking current flows through the low impedance pathprovided by the condenser 17 to Winding 35 while the remainder flowslthrough the parf allel path providedby-the filament 25 and resistance29. In other respects, this set is the same as that shown in Fig. 3.v

Fig. 5 shows a set arranged for amplifying both transmitted and receivedenergy. rlhe arrangement of this 'set is in general similar to that ofthe two-way one lelement type repeater circuit, the transmitter-receivercircuit 48 composed of the magnetic transmitter 39 and the receiver 15connected in series to one lwinding of the transformer 40 beingbaltraced from the positive circuit of the central battery over line 6,upper contact switchhook 25, rheostat 27, retard coil 18, filament 28,resistance 29, connection 47 back over line 6 to the negative terminalof central battery. The space current circuit may be traced from thepositive terminal of the central battery over line 6 through thewindings of the bell 26, primary of transformer 42, anode 30 ofimpedance of the transmitter-receiver circuitv 48 as seen through thetransformer 41, being balanced with that of the line 6, there is nodifference of potential between the terminals of the primary winding ofinput transformer 44 and, therefore, no amplified energy is fed backinto the tube 13 so as to cause singing.

This invention is not limited to the einbodinieiits shown which may bevariousl modified without departing from the spirit of the invention asdefined in the appended claims. t

What is claimed is:

1. In combination, an electron discharge device having input and outputterminals, a space current circuit and a cathode heating circuit, areceiver connected to the output terminals of said device for receivingamplified signals therefrom, a source of direct current remote from saiddevice, aline connecting said source and said device for supplyingdirect current and for transmitting signaling current to said device,means for connecting said discharge device to the line -to amplify theincoming signals transmitted f over said line, and connections forsupplying anda transformer for connecting the line to the inputterminals of the device and having such a ratio as to stepeup thevoltage of the line.

4. A telephone system comprising a central station having a source ofdirect lcurrent, a line from said station for supplying direct currentand for transmitting signaling current, a ,telephone substation,coinprising an electron discharge device having input and outputterminals and a thermionic cathode, a receiver associated with theoutputterminals of said device, a transmitter,

connections from said line for supplying drect current to saidtransmitter and said cathode in series, said Aconnections including aninducta'nce for preventing the ow of Signaling current therein,connections in para lel with a portion of said irst connectionsincluding the inductance and the cathode for transmitting signalingcurrent from said transmitter to said line, said last connectionsincluding a condenser to prevent the flow of direct current therein,connections from said line for supplying spacecurrent to said device,sad connections including an inductance, and connections from said lineto the input terminals of said device for supplying sivnalin currentthereto.

5. telep one system according to claim 4 in which the substationincludes a transformer for connecting the line with the input terminalsof the electron discharge device, and an impedance associated with aportion of the primary Winding of said transformer for rendering saidcircuit antiside tone.

In witness whereof, I hereunto subscribe my name this 16th day ofJanuary, A. D.,

' JOHN W. FOLEY.

